Syntheses, Structures, Selected Physical Properties, and Band Electronic Structures of the Bis (ethylenediseleno) tetrathiafulvalene Salts (BEDSe-TTF)(2)X, X- = I-3(-), Aul(2)(-), and IBr2-

Three bis(ethylenediseleno)tetrathiafulvalene (BEDSe-TTF) based salts, (BEDSe-TTF)(2)X (X- = I-3(-), AuI2-, and IBr2-), have been prepared by electrocrystallization and characterized by X-ray crystallography, electrical conductivity measurements, variable-temperature electron spin resonance studies, and FT-IR reflectance measurements. The triclinic (space group PI) room-temperature lattice parameters for the three salts are as follows: beta-BEDSe-TTF)(2)I-3 alpha = 6.781 (2) angstrom,b = 8.767 (3) angstrom, c = 16.023 (5) angstrom, alpha = 89.68 (2)degrees, beta = 94.76 (2)degrees, gamma = 110.66 (2)degrees, V = 887.9 (5) angstrom(3). (BEDSe-TTF)(2)AuI2: alpha = 7.614 (1) angstrom, b = 8.341 (2) angstrom, c = 15.538 (4) A, alpha = 77.56 (2)degrees, beta = 98.31 (2)degrees, gamma = 112.71 (2)degrees, V = 886.9 (4) angstrom(3). beta'-(BEDSe-TTF)(2)IBr2: alpha = 6.863 (2) angstrom, b = 10.065 (3) angstrom, c = 13.183 (3) angstrom, alpha = 87.94 (2)degrees, beta = 100.49 (2)degrees, gamma = 98.84 (2)degrees, V = 884.8 (4) angstrom(3). At room temperature, beta-(BEDSe-TTF)(2)I-3 is metallic and (BEDSe-TTF)(2)AuI2 and beta'-(BEDSe-TTF)(2)IBr2 are semiconductors. Antiferromagnetic couplings were observed in both Aul(2)(-) and IBr2- salts at 20 and 12 K, respectively. Tight-binding band calculations were performed on the donor layers of the (BEDSe-TTF)(2)X salts in an attempt to understand the electrical properties. The relationships between the crystal structures, physical properties, and band electronic structures are discussed.